Luckuly BTC can't just disappear so they are either still in your Bitcoin wallet or they arrived at your Bisq internal wallet, but Bisq is not showing it.
You can try resyncing with the Bitcoin network by deleting the SPV chain file in Settings. If that doesn't change the balance try using cmd+e
As a last resort you can always export your private keys by removing the wallet password and pressing alt+j.
So no need to worry, as long as you have your seed words your funds are safe.
Best regards,
Aleksej